Various medical devices have been developed for the delivery of therapeutic agents to the body. In accordance with some delivery strategies, a therapeutic agent is provided within a polymeric matrix coating that is associated with an implantable or insertable medical device, for example, a vascular balloon catheter or a stent. Release of therapeutic agent from the coating of such devices is, in general, governed by simple diffusion processes. In order to administer a large initial drug release after the device is positioned, the matrix is commonly loaded with a large amount of drug, or the device is dipped into a drug solution immediately prior to insertion. Unfortunately, a significant amount of drug may be washed from the surface of the device between initial insertion and ultimate placement of the device. Such premature release introduces a degree of imprecision with respect to the amount of drug that is dispensed at the placement site, and it results in drug administration to regions of the body other than the placement site—a result that becomes more and more undesirable with increasing drug toxicity.
Accordingly, there is presently a need in the art for devices and methods whereby substantial amounts of drug are released only after the medical device is placed at the site of interest. The present invention addresses these and other needs in the art.